This invention relates to the disconnection of landing strings from tubing hangers in subsea wells, and their subsequent reconnection.
The tubing hanger landing string is used to install, retrieve or work on a tubing hanger. When locked to the tubing hanger it sits within the blowout preventer (BOP) stack. One of the main functions of the BOP is to be able to isolate the well and permit disconnection of the riser via a lower riser package on the BOP. This must be done rapidly in emergencies, such as when a drilling or service vessel from which the riser is deployed is driven off station in bad weather.
In order to allow emergency riser disconnection during tubing hanger operations, landing strings have previously been designed with either a hydraulic latch or shearable joint (shear sub), or both. There are advantages and disadvantages to either option. The hydraulic latch is advantageous in that once disconnected it is quick and simple to reconnect. The disadvantage is that it adds equipment cost and operational complexity. When an emergency arises, the hydraulic latch requires a complex decision process, i.e. operate hydraulic controls at the surface to disconnect landing stringxe2x80x94waitxe2x80x94lift landing string clear of BOPxe2x80x94initiate BOP closure and then disconnect the riser at the lower riser package. The advantage of the shear sub is that during an emergency, all that is required is to initiate BOP closure and disconnect. The BOP shear rams are used to sever the shear joint, disconnecting the tubing hanger landing string. Together with other closure elements of the BOP, the shear rams also act to close in the well, allowing disconnection of the riser containing the severed landing string. This is clearly a simpler and safer operation, less prone to errors. The disadvantage of the shear sub is that following a shear and disconnect, costly and time consuming recovery operations are required to reconnect to the well.
It would be desirable to provide equipment on the landing string which can be used simply and rapidly to disconnect from the tubing hanger but which can be reconnected again with minimum time and effort.
The present invention provides a coupling comprising a first part connected in use to a tubing hanger landing string and a second part connected in use to a tubing hanger, the first and second parts being disengageable from and re-connectable to each other, the coupling comprising a disconnection mechanism whereby, with the tubing hanger landed, the disconnection mechanism may be positioned within a BOP so as to be non-destructively engageable by closure elements of the BOP; such non-destructive engagement causing the mechanism to disengage the connector parts so as to separate the landing string from the tubing hanger.
The coupling may be directly connected to the tubing hanger in use, or it may comprise intervening components such as a tubing hanger running tool and/or a tubing hanger orientation joint.
The BOP closure elements may be, for example, pipe rams, which may operate a control element of the coupling arranged to control an actuator for the disconnection of the coupling. The control element may be, for example, an electrical switch or a hydraulic valve. The actuator may be an electrical, hydraulic or electro-hydraulic actuator operatively connected to a latch which releasably holds two parts of the coupling in engagement with each other.
Preferably, however, the mechanical action of the BOP closure elements as they engage the coupling itself causes disconnection of the coupling. For example, the coupling may comprise two parts releasably held in engagement with each other by collet fingers, pipe rams of the BOP acting upon the collet fingers to cause the disconnection. The pipe rams may act directly upon the collet fingers, or the rams may act on intermediate components such as actuator pins and a split ring which in turn act upon the collet fingers.
Further preferred features and advantages of the invention are set out below in the following description of illustrative embodiments, made with reference to the drawings.